Device for receiving and recording telegraphic symbols



Nov. 3, 1942. K. B. PALME 2,300,453

DEVICE FOR RECEIVING AND RECORDING TELEGRAPHIC SYMBOLS Filed Jan. 30,1941 2 Sheets-Sheet 1 Inventor.-

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Patented Nov. 3, 1942 DEVICE FOR RECEIVING AND RECORDING TELEGRAPHICSYMBOLS Karl Bertil Palme, Bofors, Sweden, assignor to Bolinders FabriksAktiebolag, Stockholm, Sweden, a corporation of Sweden ApplicationJanuary 30, 1941, Serial No. 376,707 In Sweden November 6, 1939 4Claims.

The invention relates to a device for receiving and recordingtelegraphic symbols, which is to a large extent independent ofinterference and gives a particularly clear script, in which the lengthof the different symbols and the distance" between them can beestablished with considerable accuracy, a feature which can also be ofvery considerable importance, inasmuch as it renders possible theidentification of different transmitters by characteristics peculiar toeach telegraphist. By reason of the fact, moreover, that the deviceoperates with practically no lag, the possibility is also afforded ofregistering symbols clearly even when coming from high speed mechanicaltransmitters.

The fact that the apparatus is independent of interference is based onthe feature that only the amplitude peaks of the telegraphic symbolimpulses are utilized for actuating the telewriter, which according tothe invention is arranged to be set into operation only by suchtelegraphic symbol impulses as have an amplitude exceeding apredetermined threshold value lying above the normal interference level.

According to one particularly appropriate form' With these and otherobjects in view, referencemay now be had to the accompanying drawingsfor a more detailed description of the invention.

In the accompanying drawings, Fig. 1 shows a circuit diagram for thereceiving and recording device according to the invention, thetelewriter proper being represented in a side elevation. Fig. 2 shows avalve characteristic curve, whilst Figs. 3 and 4 show the telewriterproper and the arrangement for operating it: Fig. 3 represents a frontview, partly in section along the line III-III in Fig. 1, and Fig. 4 aview in cross-section along the line IVIV in Fig. 3. Fig. 5 shows adevice for damping the writing device, and Fig. 6 shows a telegraphedmessage strip with the symbols as written in the apparatus, according tothe embodiment shown. Fig. '7 shows an electromagnetic system of atelewriter, said system being known per se. Figs. 8-10 show anelectromagnetic system of a tele writer according to the invention.Figs. 8 and 9 represent two side elevations, perpendicular to oneanother, and Fig. 10 a view in cross-section along the line X-X in Fig.8. Fig. 11 shows a modification of the armature used in the em--bodiment shown in Figs. 8-10.

' of the transformer 4.

The telegraphic symbol impulses are received in a receiver I, whichtransforms the received impulses into audiofrequency A. C. impulses,which are applied to a potential divider 2, from which they are taken ata tapping 3 and at suitable strength to a transformer 4, the ends of thesecondary winding of which are connected to the anodes of a double diodevalve 5. The cathode of the double diode valve is connected over aresistance 6, in parallel with a condenser 1 to the central tapping 8 ofthe secondary winding The A. C. impulses rectified by the double diodevalve 5 charge the condenser 1, and in order that such charging may takeplace rapidly in relation to the length of the A. C. impulses, the timeconstant of the circuit 6, I has been made small in relation to thelength of the impulses, e. g. to about 6 second.

The voltage across the condenser l is connected over a large resistance2|] of about 1 megohm to the third grid 9 in the hexode section of atriode-hexode valve Ill. The triode section of this electronic valve I0is connected up as an oscillator, the frequency of which is determinedby a circuit ll, consisting of a shunt connection of a transformer l2and a condenser I3. The circuit II is over a condenser l4 connected withthe grid l5 in the triode section of the triodehexode valve. Theoscillations from the oscillator system are applied to the hexodesection of the valve ID, by the first grid H5 in the hexode section andthe grid IS in the triode section being interconnected.

In series with the parallel connection of the resistance 6 and thecondenser l is a voltage which is negative in respect to the cathode llof the triode-hexode Valve, and in the embodiment of the inventionconcerned in the present case this voltage is taken from the gridconnection of the oscillator system over a resistance l8 and a condenserl9 connected to earth. This negative bias voltage which is in serieswith the voltage produced by the incoming telegraphic symbol impulsescan, of course, also be obtained in some other way, for example by meansof a battery. In Fig. 2 is shown the slope of emission characteristic 8of the hexode, for the first grid 16, with regard to the anode current,plotted as a function of the negative bias voltage v s on the third grid9. It will be appreciated from this characteristic that if the biasvoltage on the third grid is kept at point U gB, the slightestalteration of the voltage in a positive direction, for example bycharging of the condenser 1 due to incoming impulses, such asinterference or effective impulses, w ll result in the hexode section ofthe valve lil supplying anode current which roaches i s maximum valuewhen the negative bias Voltage on the third. grid has risen to zero.Further increase of the signal voltage will not cause the anode currentto increase.

If, however, the negative bias voltage on the third grid is selected asbeing equal to v"g3, the voltage produced over the condenser I by theincoming impulses must exceed the difference between the absolute values17"g3 and 'U'g3 before the hexode will supply any anode current. Thissystem is, accordingly, utilized in this case for suppressinginterference impulses, by the negative bias voltage being selected sohigh that interference within the normal interference range will notremove this negative bias voltage.

Any considerable variations of the positive voltage across the condenserI, which might possibly occur, will not be noticeable on the third gridIS in the hexode section of the valve [9, owing to the voltage drop ofthe grid current in the large resistance 29. Any variations on the partof the incoming impulses will not, therefore, become noticeable as faras the anode current from the hexode section in the valve I9 isconcerned.

In order to render it possible to regulate the negative bias voltage inthe circuit shown, the voltage can possibly be taken from a point on thegrid leakage resistance 2i.

If the voltage across the condenser produced by the impulses taken fromthe potential divider is sufficiently large to remove the negative biasvoltage altogether, the anode current of the hexode will be totallyindependent of fluctuations in the amplitude of the incoming impulses aslong as the voltage produced across the condenser I is adequate toremove the negative voltage altogether.

The anode current supplied by the hexode section of the valve 9 due toincoming telegraphic impulses and having the frequency determined by theoscillator circuit H is taken out over a condenser 22 and a potentialdivider 23 and amplified in an amplifier 24, which duly supplies theoperating coil 25 of the actual telewriter over a condenser 26. Theanode 21 of the hexode section of the valve It is connected with thesource of anode voltage over a resistance 28 and the anode 29 of theamplifier 24 is connected with the same over a choke coil 39.

Reference is directed to Figs. 1 and 3-5 with regard to the telewriterand the device for operating it. The operating device comprises a U-shaped magnet 3i, to which are fixed the pole plates 32 and 33 ending inpole shoes 34. The pole shoes are kept at a constant distance from oneanother by means of the non-magnetic distance piece 35. The armature 3Soscillating in front of the air gap between the pole shoes 34 comprisesan oblong piece of iron fixed to a phosphor-bronze spring 39 heldbetween the frame block 31 and a plate 38. The armature 36 passesthrough the coil 25 and is actuated by the oscillations applied to thiscoil having the frequency determined by the oscillator circuit ll (Fig.1).

Fixed to the armature 33 is a narrow metal plate beam piece 49, made atone end into the form of a cylinder 4!, into which is introduced one endof a piece of rubber tubing 42, e. g. socalled valve rubber tubing. Therubber tubing is guided by an arm 43 fixed to the block 31 and providedwith a recess to accomodate the tubing. Ink is conveyed through thetubing from an ink reservoir 44 to a capillary tube point 45 to theabutment 49.

of glass, which when not in use lies against the center of the telegramstrip 48. The telegram strip is fed forward in the direction asindicated by the arrow.

When A. C. is applied to the coil 25, due to the arrival of telegraphicsymbol impulses relieving blocking of the anode current of thetriodehexode valve l0 in the hexode section, the armature 36 will startoscillating in front of the air gap between the pole shoes 34 of themagnet 3 I. Since the capillary tube point is in fixed connection withthe armature it will simultaneously inscribe oscillations on thecontinuously fed telegram strip. As stated above, Fig. 6 shows thisstrip inscribed in the manner referred to. Viewed from the left, therewill be seen on the telegram strip two dots, one dash and one dot, andknowing the oscillation frequency of the armature, which ispredetermined by the frequency of the oscillations applied to the coil25, and hence by the frequency of the oscillator system, it is possibleto read off with accuracy the length of the different symbols on thetelegram strip by counting the number of oscillations. For determiningthe length of the different symbols, therefore, it is not necessary toknow the feeding speed of the telegram strip, and it is immaterialwhether this speed varies or not. It should be quite obvious that withthe system described above it is possible to determine the length of thedifferent symbols with considerably greater ease and accuracy than hashitherto been the case. The possibility of obtaining clear registrationof symbols from rapid mechanical transmitters can be afforded byimparting a high frequency of oscillation to the inscribing point andsimultaneously causing the paper strip to be fed forward at a relativelyhigh speed. Fig. 6, for instance, shows that the second dot has lastedtwo periods longer than the first dot. By varying the frequency of theoscillator system facilities are also made available for adapting thefrequency of the telewriter to different conditions, e, g. the feedingspeed of the telegram strip.

The accuracy with which the length of the different symbols can be readoff is also to a considerable extent dependent upon the building-up timeof the oscillating system connected to the inscribing point 45, i. e.the time taken for it to build up or get into full constant operation.To attain rapid building-up it is necessary that the ratio between thefrequency of the applied oscillations and the natural frequency of theoscillating system shall be less than 1. In addition, the oscillatingsystem should be intensely damped. For this purpose there is fixedlyconnected to the armature 36 over an arm 47 a plate 48 moving betweentwo abutments 49, 59 for example of leather, one of which 49 is fixed toa support 5| and the other attached to a spring 52 fastened to a fixedsupport 53. The abutment 59 can by means of a screw 54 be pressed moreor less forcefully against the plate 48 contiguous The abutments 49, 50,therefore, exercise a kind of braking action on the plate 48 and thusdamp the entire oscillating system. Of course the damping device iscapable of being designed in other ways, without the function of theapparatus being in any way altered in principle. The essential thing isthat the oscillating system shall be intensely damped, since otherwisethe accurate determination of the length of the different telegraphicsymbols will be rendered more complicated and may possibly even be lostsight of altogether, as will be more exactly described in the following.

In telewriters of the described kind it is very important that thewriting device rapidly reaches the end state, i. e. the oscillationapplied to said device shall preferably be completely built up duringthe first half-period of the oscillation. In addition the problem is toobtain a sine shaped script having a great amplitude and a highfrequency. Such a script is most easily obtained by means of an undampedsystem oscillating in resonance. The oscillation of such a system,however, is very slowly built up to the end state.

By increasing the damping of the system, which causes increase ofapplied energy, the system can rapidly reach the end amplitude.

Dependent on the phase, in which the oscillation begins, the firstamplitude may be somewhat greater than the end amplitude. If, however,the applied frequency is decreased to a value below the naturalfrequency of the system, e. g. down to 50%, the first amplitude becomesapproximately equal to the amplitude in the end state, provided that thedamping is appropriate.

If, therefore, an electromagnetical operating system is desired, whichby a given mass of the load, for example a style, has a great amplitude,e. g. at a frequency of 200 c., the problem is to produce anelectromagnetical system having a mechanical natural frequency of about350 c. and requiring the least possible energy.

A solution of this problem is illustrated in Fig. 7 showing a knownembodiment in section. Between two pairs of poles 55, 56 and 51, 58respectively an oblong tongue 59 is oscillating. The

tongue is fixed to a plane phosphor-bronze spring 65, extending normallyto the plane of the paper. The tongue or the armature 59 can thenvibrate round an axis lying perpendicularly to the plane of the paperand is driven by the electric energy supplied to a coil divided into twosections 6| and 62.

Supposing the damping is so chosen, that at each moment the deviation isproportional to the current in the coil, the moment of the current ateach moment must balance the elasticforce of the system. The naturalfrequency 1 of the system is D indicates the returning moment (theelastic force) and 0 the moment of inertia of the armature system.

Further thedeviation is where k indicates an apparatus constant and inthe ampere-turns.

The essential thing is then to make lc/D large and even \/D/0 large, ifit is desired that the system shall have a high natural frequency. Thusit is to be large and 0 small.

In the arrangement shown in Fig. 7 and operating with very small airgaps is will be large.

The electromagnetical operating system shown in Fig. 7, however, suffersfrom certain disadvantages, which are to be removed according to theinvention. The supporting spring 59 for instance takes up space in thelongitudinal direction of the tongue, encroaching upon the space at thedisposal of the coils. The necessity to divide up the winding into twocoils requires an increased insulation quantity, which further increasesthe space required for the necessary ampere-turns. Consequently, thetongue must have a relatively great length for the necessary winding.'Therefore, the moment of inertia of the armature system becomes large,e. g. it grows proportionally to the third power of the length of thetongue.

It is a further object of the present invention to remove saiddisadvantage and to render possible a reduction of the moment of inertiaand an increase of the winding space. An embodiment fulfilling saidrequirements is shown in Figs. 8-10.

The permanent magnet system consists of one or more permanent magnets,e. g. cylindrical hollow bars 19, 86, connected in shunt and enclosingbolts of non-magnetic material. The same poles of the magnets are turnedin the same direction so that each of the plates 63 and 64 of soft ironlimiting the whole system has its polarity, Pole shoes 65, 61 and 66, 68are formed of down bent parts of these plates 63 and 64 respectively insuch a manner that they stand opposite one another. The pole shoes 65and 66 are formed from the plate 63 and for example constitute southpoles, while the pole shoes 61 and 68 are formed from the plate 64 andconstitute the north poles. The air gaps between these pairs of poles65, 61 and 66, 68 respectively are kept constant by means of distancepieces 69 and I0 respectively of non-magnetic material. The armature isfastened to a phosphor-bronze spring 12 fixed in two supports 13 and 14secured to the plate 63. The armature consists of a narrow oblong part,at one end of which a lateral projection 15 is provided and at the otherend of which, in opposite direction, a projection 16 extends, so thatthe armature receives a Z-shape. The projections extend towards the polepairs 65, 61 and 66, 66 respectively without contacting the latter, sothat the projections can vibrate freely round the fastening spring 12 asan oscillation axis. The operating coil 11 is arranged round the narrowcentre part of the armature. Dotted lines illustrate at 18 how a writingdevice of the kind as above described may be fixed to the armature.

The embodiment above described has the advantage that the narrow part IIof the armature can be made considerably long without increasing theinertia moment. the latter being substantially determined by theprojections 15 and 16. Thereby a great winding space is gained withoutincreasing the moment of inertia. An operating system of the describedkind can, for a given purpose, be produced with as great an apparatusconstant as before but with a considerably smaller moment of inertia ashitherto could be reached. Therefore, an operating system of this kindis very suitable for all fields of application, where it is desired tohave an oscillation of a great amplitude at a high frequency and of arapid building-up-process of the oscillation.

Fig. 11 shows a modification of the armature used in the embodimentshown in Figs. 8-10. In

Fig. 11 the projections 15a and 16a from the armature 1 la extend in thesame direction. In this case the pairs of magnet poles must be arrangedso that the poles are reversed at one end as compared with theembodiment shown in Figs. 8-10.

According to still another modification not shown projections in twoopposite directions can be provided at each end so that the armaturetakes the shape of an I. The arrangement of the magnet system thenbecomes more complicated but no difiiculty seems to arise for thoseskilled in the art.

The embodiments of the invention as illustrated in the drawings anddescribed in the press cut specification are shown only by way ofexample and do not involve any limitation of the invention to thedetails presented in these embodiments. The invention does also embracea writing device which is arranged to be set into vibrations following acourse at right angles to the direction of feed of the telegram stripand lying in the plane of the paper, even though such a writing devicemay not necessarily be combined with an interference suppressingapparatus according to the invention.

What I claim is:

1. A device for receiving and recording telegraphic symbols, comprisinga receiver of telegraphic impulses, a local oscillator system, atelewriter adapted to record said symbols in the form of oscillations,means for operating said telewriter with the frequency of saidoscillator sys tem, interference-blocking means, comprising anelectronic valve, a control grid in the same, controlling the operationof said telewriter, means for applying a negative bias voltage to saidgrid, and means for producing a positive voltage, determined by theamplitude of the telegraphic symbol impulses received, in series withsaid negative bias voltage, means whereby the negative bias voltageblocks the anode current of the electronic valve until the positivevoltage has risen to the value corresponding to the predeterminedthreshold value, whereby only impulses exceeding said value cause thetelewriter to operate and to record the telegraphic symbols in the formof groups of oscillations having the frequency of said oscillatorsystem, which frequency is chosen sufficiently high in order that itsperiod will only constitute a fraction of the duration even of veryrapid impulses.

2. A device as claimed in claim 1, in which said means for producing apositive voltage comprises a parallel connection of a resistance and acondenser, the time constant of which connection is low in relation tothe minimum length of the telegraphic symbol impulses.

3. A device as claimed in claim 1, in which a large resistance isconnected nearest said control grid in series with the means for applyina positive and negative voltage to said control grid for damping largevariations of positive voltage.

l. A device as claimed in claim 1, in which means are provided fortaking the negative bias voltage from the local oscillator system.

ARL BERTIL PALME.

